1. Field of the Invention
The present invention concerns a magnetic disk recording apparatus having magnetic heads for reading or writing data from or onto disks, and more particularly a technique for controlling the write currents supplied to magnetic heads to write data on the magnetic disks.
2. Description of the Related art
A magnetic disk recording apparatus such as hard disk drive (HDD) or a floppy disk drive (FDD), is generally used as an auxiliary memory device for a computer system. Especially, an HDD usually has a capacity to stably store a large amount of data and to make it possible to access stored data at a great speed. Since the write density of the magnetic disks of an HDD has continuously increased in order to increase the data storage capacity, the magnetic heads must be made with a high precision. To this end, the use of thin film heads has been increased in order to obtain a high data recording density. However, the thin film heads suffer from various problems connected with the characteristics of head poles. One of the typical problems is a phenomenon called "Barkhausen Noise", which is generated when an HDD transits from a writing phase to a reading phase; this noise is also called popcorn noise or wiggle noise.
The cause of such noise will be considered with reference to FIG. 1 for illustrating the writing operation timing according to a write control sequence used in HDDs, and to FIGS. 2A and 2B for illustrating a partial cross sectional view of a thin film head core to showing the changes of the magnetic polarity arrangement before and after cutting off the write current. In FIG. 1, reference numeral R/W represents a read/write mode signal, which is "high" in a read mode and "low" in a write mode. Reference numeral WDI represents encoded digital data recorded on a magnetic recording disk. The write current is supplied to the coil of a head according to the write digital data WDI, normally having a constant value. The disk is covered with a magnetic layer magnetized by the magnetic field generated by a head. A read signal is an analog signal picked up by a head from a disk in the read mode. In FIGS. 2A and 2B, reference numeral 2 indicates the coil of a head, which supplies the write current to the head to write data on a disk as shown in FIG. 2A. FIG. 2B illustrates the state of the head and the disk after cutting off the write current. Reference numerals 4a and 4b indicate magnetic poles, and the numeral 6 indicates the magnetic layer covering a disk.
In the write mode, an HDD supplies the write current to the coil of a head 2 according to the write data, so that the magnetic polarity elements of the magnetic poles 4a and 4b are arranged in a given direction, thereby producing a magnetic field, as shown in FIG. 2A. The magnetic field magnetizes the magnetic layer deposited on a magnetic recording disk 6 to write data. When the write current is cut off to end the data write mode, the regular arrangement of the magnetic polarity elements are broken due to an entropy increase as shown in FIG. 2B, thereby changing the magnetic field, which causes the Barkhausen noise to usually be prolonged for about 7 .mu.s-10 .mu.s until the head is stabilized.
Presently, the heads of an HDD are commonly used for both read and write operations. Hence, the Barkhausen noise is usually contained in the read signal picked up from a disk immediately after the HDD has transited from the write mode to the read mode. The Barkhausen noise is indicated by reference numeral S.sub.n in FIG. 1. Such noise distorts the waveform of the read signal causing data errors. The Barkhausen noise is always generated when a thin film head transits between the write and the read mode although the amount differs more or less according to the characteristics of the heads.
The Klaassen, et al. patent, U.S. Pat. No 5,168,395, discloses a current tapering circuit which gradually reduces the write current in a recording head with a ramp or decaying exponential termination. The technique shown in Klaassen et al. depends upon a monotonically decaying taper circuit having a time constant that is at least as long as a characteristic relaxation time of the domain walls in the driven magnetic recording head. However, Klaassen, et al. does not teach or suggest the specific features of the write current adjustments circuit of the present invention.
The following additional patents each disclose features in common with the present invention but are not believed to be as pertinent to as a Klaassen, et al. reference noted above: U.S. Pat. No. 5,067,032 to Ida, entitled Head Driver, U.S. Pat. No. 5,038,230 to Kusunoki et al., entitled Method Of Accurately Executing Read Access And Magnetic Recording/Reproducing Apparatus Therefor, U.S. Pat. No. 4,479,151 to Lia et al., entitled Magnetic Recording Of Digital Signals On A Magnetic Medium, U.S. Pat. No. 4,428,008 to Fawkes, entitled Electronic Switching Circuit For Use In Magnetic Head Drives, U.S. Pat. No. 3,869,714 to Schneider et al., entitled Method And Apparatus For Controlling The Risetime Of A Digital Magnetic Recording Waveform, U.S. Pat. No. 5,485,320 to Vogel et al., entitled Method And Apparatus For Adjusting Asymmetric Recording Signals, U.S. Pat. No. 5,483,390 to Jaffard et al., entitled Device For Switching A Video Tape Recorder Head To Write/Read Mode, U.S. Pat. No. 5,461,517 to Suda et al., entitled Magneto-Resistance Effect Type Of Recording/Reproducing Head, U.S. Pat. No. 5,436,772 to Sekiya et al., entitled Magnetic Recording And Reproducing Apparatus Having Magneto-Resistance Effect Element, U.S. Pat. No. 5,392,172 to Yoshinaga et al., entitled Magnetic Head Circuit Having A Write Current Changeover Circuit With A Clamp Voltage Depending On Write Current For High-Speed Data Transfer, U.S. Pat. No. 5,392,169 to Argyle et al., entitled Electrical Means To Diminish Read-Back Signal Waveform Distortion In Recording Heads, U.S. Pat. No. 5,359,467 to Nakamura, entitled Write Circuit Providing Selective Waveform Correction Based On Recording Density, And Magnetic Recording Apparatus Employing The Write Circuit, U.S. Pat. No. 5,331,479 to Madsen, entitled Capacitor Assisted Low Voltage Write Circuit, and U.S. Pat. No. 5,307,214 to Magnetic Recording Apparatus.